The promise of using a fuel cell to power portable electrical devices has been dangled in front of us for many years, but we still seem some way from easy, safe devices that generate power by consuming fuel in an electrochemical reaction instead of storing externally generated electrical energy.  

But we're getting closer.

US consumers can now buy an external power source for mobiles, mp3 players and portable game consoles that promises 30 hours of talk time or 60-80 hours of music from a single fuel cell. It's called the Power Pack and comes from US/Israel-based fuel cell developer Medis Technologies and it's about the size of one of the portable USB-powered hard drives many of us now carry around.

The Power Pack is uses an undisclosed chemical - according to the manufacturers it's a  'proprietary Direct Liquid Fuel Cell (DLFC) technology' and 'the underlying chemistry is a direct liquid borohydride technology'. There has been some published research to indicated that it's a viable method, noting that 'borohydride and methanol fuel cells... exhibit similar cell voltages, current and power densities' so it's a promising path to take even if we'd be better off with openly published and freely available technologies.

The Power Pack is on sale for  $25 in the US, with replacement cells for $20, and the company has had enough sense to set up a recycling programme for used cells, although at the moment it's rather limited.  They are also promising a slimmer model using solid fuel, and a higher-power version for use with laptops.

Direct electricity generation in our devices is clearly the way to go, given the losses in transmission that Jonathan has been talking about elsewhere, so we need to watch this area closely. And, of course, we need to ensure that the total cost of the cell - manufacture, distribution, disposal - is taken into account when we calculate the real energy costs of this and other alternative technologies.